Interactions among T cells, B cells, and antigen-presenting cells initiate immune responses which are mediated and regulated by cytokines and by cell surface interactions. Subsets of CD4+ T cells have been identified on the basis of secreted lymphokines. Subsets of CD8+ T cells have not been characterized in detail. The general goal of the research proposed in Project 2 is to characterize the mechanisms that regulate the functions of T lymphocytes which are responsible for rejection of allografts, with emphasis placed on CD8+ T cells. We will define CD8+ T cell subsets reacting to individual major histocompatibility complex (MHC) antigens as well as determining the mechanisms that control the responses of these T cell subsets. We will study mainly the response to class I MHC antigens, particularly H-2Ld. Three Specific Aims are proposed to accomplish this general goal: 1) To determine the cytokines and cell surface molecules that are involved in activating naive and primed CD8+ T cells reactive with H-2Ld class l MHC antigen, using T cells from transgenic mice whose CD8+ T cells express an antigen-specific, transgenic (Tg), alpha/beta T cell receptor (TCR) which reacts with H-2Ld alloantigen. Naive CD8+ T cells will be obtained from unprimed spleen and lymph nodes. Sensitized CD8+ T cells will be obtained from lymph nodes draining the site of a rejecting skin allograft or from the spleen following intraperitoneal injection of allogeneic cells. The role of specific lymphokines (including IL-1, IL-2, lL-4, lL-1O and lL-12) and cell surface molecules (including B7-1, B7-2, CD28, CTLA-4, LFA-1, ICAM-1) in activation for proliferation, lymphokine production, and acquisition of cytolytic activity will be determined, using neutralizing monoclonal antibodies (mAb) and various populations of antigen-presenting cells (APC); 2) To derive clones representing various CD8+ T cell subsets and compare the mechanisms that regulate various functions of these clones with those controlling naive CD8+ T cells. The experiments proposed to accomplish Specific Aim 1 should define the essential conditions (lymphokines and cell surface molecules) for stimulating CD8+ Tg T cells to produce those lymphokines that have distinguished subsets of CD4+ T helper (Th) cells, namely interleukin (IL) 2 and interferon-gamma (IFN-gamma) for Th1 and IL-4, lL-5, lL-6, and lL-10 for Th2. Using this information, we will define conditions that lead selectively to activation of one or another subset, and we will derive clones of CD8+ Tg T cells that secrete different lymphokines arrays. We will determine functions of clones representing CD8+ subsets, measuring lymphokine production, provision of B cell help, and cytolytic activity mediated by perforin and Fas. We also will evaluate the ability of various CD8+ subsets to regulate responses of naive CD4+ and CD8+ T cells and CD4+ and CD8+ clones in vitro; and 3) Based on the information obtained through the other Specific Aims, to develop strategies for suppressing allograft rejection. Possible therapies include the use of mAb reactive with particular cytokines and/or mAb or other reagents that react with cell surface structures on the particular T cell subsets or APC.